Lower Kihansi hydroelectric project

Name of Project:

Lower Kihansi hydroelectric project



Country:
Tanzania

Client:
Tanzania Electric Supply Company Ltd.(TANESCO)

Construction period:
July 1995 - February 2000

The Lower Kihansi hydroelectric power plant is located about 450 km southwest of the capital Dar Es Salaam and 80 km south of the city of Iringa. The main works of the project are described below.

Dam and intake structure
The concrete gravity dam, which created a reservoir of one million cubic meters of water, has a maximum height of 25 m and a crest length of 200 m.
The middle portion of the dam consists of an open spillway that is 70 m long, designed for a discharge capacity of 470 m³/s.
A consolidation grout curtain was made along the entire length of the dam.
Downstream of the spillway, work was done to protect against erosion with concrete retaining walls and rip-rap lining on the slopes.
The intake structure, located on the left bank of the river, is an integral part of the dam structure and incorporates a 10 x 6 m trash rack rake and a 4 x 5 m control gate.

Tunnels
The project includes the following underground structures:
a vertical shaft 5.64 m in diameter and 508 m long;
a headrace tunnel with a cross-section of 30 and 37.6 m², 2,276 m long, with a slope of 1:7, which then branches off into three reinforced penstocks having a total length of 329 m;
a main plant-access tunnel with a cross-section of 40.5 m², 1,807 m long, which has also
additional sections, for an overall length of 2,280 m, allowing access to the transformer vaults;
five outlet pipes with a cross-section of 22 m² and a discharge tunnel with a cross-section of 34 m², for a total length of 2,368 m;
cable tunnel 1,765 m long;
other service tunnels of variable cross-section, for a total length of 526 m.
A special settling and collection structure for coarser material was made in the reinforced end portion of the headrace tunnel. Another penstock departs from the underground settling basin for a future increase in the plant's capacity.

Underground power plant and transformer vaults
The plant has an initial capacity of 180 MW, with three vertical Pelton turbines which utilize a gross drop of 853.5 m. It will have a final installed power of 300 MW with five generator units. The underground power plant is 70.3 m long, 12.6 m wide, and has a maximum height of 33.6 m.
Turbines and generators located in the plant are connected to their corresponding transformer vaults by three busbar tunnels.

MAIN TECHNICAL DATA:
Surface earth excavation: 968,000 m3
Surface rock excavation: 63,000 m3
Underground excavation: 346,800 m3
Embankments and fill: 441,000 m3
Surface concrete: 58,830 m3
Underground concrete: 14,895 m3
Sheet piling: 4,240 m2
Road base and sub-base : 29,900 m3

Last update: 18/09/2013